1. Field of the Invention
The present invention relates generally to a storage apparatus such as a magnetic disk apparatus using a spin valve head as a read head integrated with a write head, and more particularly to a storage apparatus using a spin valve head through which a sense current flows in the interference direction generating a magnetic field opposite in direction to a magnetic field in a pin layer.
2. Description of the Related Arts
With the increased capacitance of the magnetic disk apparatus, the recording density on a magnetic disk medium has become further improved. Such a high recording density that exceeds 3 Gbit/inch.sup.2 is making it difficult to use as an apparatus due to the lowering in the regenerative signal level and the degradation in the SN ratio. Thus, in order to achieve such a high recording density that exceeds 3 Gbit/inch.sup.2, the spin valve head has been put to practical use. The spin valve head basically has a four-layered structure consisting of an antiferromagnetic layer, a pin layer, a nonmagnetic layer and a free layer. This structure allows the direction of magnetization in the pin layer in contact with the antiferromagnetic layer to be fixed and prevents the free layer separated by the nonmagnetic layer from having a fixed direction of magnetization. When an external magnetic field is applied thereto in the form of a record magnetic field of the medium, the direction of the magnetic field of the free layer is determined by the external magnetic field, and a resistance value varies depending on the difference relative to the direction of the magnetic field of the pin layer. This resistance value is maximized when the directions of the magnetic field in the free layer and the pin layer are opposite 180 degrees to each other, and is minimized when they are identical. Furthermore, the spin valve head allows a sense current to flow therethrough in order to cancel an unnecessary vertical bias magnetic field which may be applied to the free layer as a result of a magnetic coupling of the pin layer which could be called a permanent magnet from its effective aspect. The direction in which the sense current flows includes two directions, that is, an assist direction generating a magnetic field in the same direction as the pin layer, and an interference direction generating a magnetic field opposite to the pin layer. Typically, the interference direction results in a larger output and smaller vertical asymmetry.
In the case of the spin valve head through which the sense current flows in the interference direction, however, a magnetic field by the sense current is generated in the opposite direction to the magnetic field in the layer, so that there arises a problem that the direction of the magnetic field in the pin layer may be offset if the temperature of the antiferromagnetic layer exceeds the blocking temperature due to the external temperature, heating of the element, static electricity, etc. In case the antiferromagnetic layer is made of FeMn in particular, the blocking temperature is as low as 150.degree. C., which may cause a serious problem. In the assist direction, on the other hand, the direction of the magnetic field in the pin layer is the same as the direction of the magnetic field generated by the sense current, so that any offset of the magnetic field in the pin layer is hard to occur.